m25

The M25 or London Orbital Motorway is a major road encircling almost all of Greater London, England. The Dartford Crossing (A282) is part of the orbital route but is not part of the motorway. The M25 is one of the most important roads in Britain and one of the busiest. The final section was opened by the Prime Minister Margaret Thatcher in 1986; on opening it was the longest ring road in Europe at 117 miles (188 km).
Patrick Abercrombie had proposed an orbital motorway around London in the 1944 Greater London Plan, which evolved into the London Ringways project in the early 1960s. By 1966, planning had started on two projects, Ringway 3 to the north and Ringway 4 to the south. By the time the first sections opened in 1975, it was decided the ringways would be combined into a single orbital motorway. The M25 was one of the first motorway projects to consider environmental concerns and almost 40 public inquiries took place. The road was built as planned despite some protest that included the section over the North Downs and around Epping Forest which required an extension of the Bell Common Tunnel.
Although the M25 was popular during construction, it quickly became apparent that there was insufficient traffic capacity. Because of the public inquiries, several junctions merely served local roads where office and retail developments were built, attracting even more traffic onto the M25 than it was designed for. The congestion has led to traffic management schemes that include variable speed limit and smart motorway. Since opening, the M25 has been progressively widened, particularly near Heathrow Airport.
In some cases, such as the Communications Act 2003, it is used as a de-facto reference to Greater London.

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